Growth and protein turnover in Atlantic salmon (Salmo salar L.); the effect of dietary protein level and protein particle size

In modern fish feeds, the protein sources consist of denaturated finely gro und ingredients. From the literature, it has been reported that use of coar sely chopped, but not denaturated, fish as the dietary protein source gave better growth performance and protein utilisation. Growth, feed utilisation and protein turnover using two different fish meal particle sizes (micro- or coarse grounded) at three dietary protein concentrations (30%, 35%, and 45%) were studied in individually tagged Atlantic salmon in a 3-month growt h experiment. At the end of the experimental period, C-14-L-lysine was inje cted intraperitonally and dorsal muscle samples were taken at 2- and 4-h po st-injection. Incorporation of C-14-L-lysine into muscle protein, RNA, DNA and water soluble protein was analysed from samples of muscle tissue. Only small effects on growth rate, feed conversion rate, protein and energy rete ntion, and nitrogen and fat digestion were found. During the growth experim ent, large individual variations in growth rates were observed, which did n ot correlate to the initial body weight. The total RNA content expressed as RNA amount per unit of DNA (RNA:DNA ratio) did not reflect the specific RN A activity, and individual growth race was not correlated to the specific R NA activity or RNA:DNA ratio and only poorly to the relative incorporation rate of amino acids. Growth rate was, however, correlated to the relative e fficiency of protein synthesis. The results indicate that the protein catab olism is more important for net protein deposition and growth than protein anabulism. (C) 2000 Elsevier Science B.V. All rights reserved.